This invention relates to a barrier film having high colorless transparency and a method for forming the same.
Barrier films have heretofore been provided. Typical coatings are of the type disclosed in British patent specification 1,086,482. It is disclosed therein that the preferred inorganic coatings are oxides of silicon and aluminum which can be deposited as transparent flexible coatings in a glassy state. Silicon monoxide or silicon dioxide are mentioned as starting materials and aluminum oxide for the aluminum coatings. This aluminum oxide is identified in Table V as being Norton Alundum #4186. This is not a pure aluminum oxide but a mixture of aluminum oxide and silicon dioxide (Al2O3 in a SiO2 binder). Zirconium oxide is also mentioned as a starting material. However, this material is not particularly suited for evaporation techniques because of its high melting temperature. Silver chloride which is also identified as a starting material is undesirable because it becomes hazy when deposited as a coating material. With respect to all of the starting materials mentioned, they are deposited as a single layer. In coating operations, the roll speed is very slow at the rate of 3 inches per minute. The single layer is also deposited to a thickness, as for example, 6000 Angstroms which is very thick. It is pointed out that the minimum thickness is 0.02 microns (200 xc3x85). Below this thickness the inorganic barrier layer is ineffectual. The tables in the British patent specification 1,086,482 disclose the barrier properties with respect to oxygen and helium, but do not address water permeability. In addition, in U.S. Pat. No. 4,702,963 there is disclosed a barrier film which is made from silicon monoxide or a suboxide of SiO2. Although this barrier film has good barrier properties, it has the undesirable feature that it has an amber color. This amber color is objectionable in many packaging applications because it obscures the true color of the product within the package. It has been found that when silicon dioxide is deposited directly on a film by electron beam evaporation no additional barrier properties are provided by the silicon dioxide. There is therefore a need for a new and improved barrier film which has a colorless transparency. In addition, there is a need to replace existing aluminized polyester and co-extruded polymeric films. Also, in view of solid waste disposal problems, there is a need to limit the use of non-recyclable plastic films. There is also a need to reduce the total volume of plastic waste which is non-recyclable by reducing the thickness and the number of plastic layers and by recycling the plastic film. Co-extruded plastic film structures are not easily recycled because of the complexity of the chemical structures in the co-extrudants. There is also a need to reduce the use of PVC and PVDC as barrier materials in film in order to eliminate migration of un-reacted monomers reaching food contents packaged within such barrier films.
In general, it is an object of the present invention to provide a barrier film having high colorless transparency and a method for making the same.
Another object of the invention is to provide a barrier film of the above character having water white high colorless transparency.
Another object of the invention is to provide a barrier film of the above character which has an overall reduced thickness.
Another object of the invention is to provide a barrier film of the above character which can run efficiently in conventional cigarette packaging machines.
Another object of the invention is to provide a barrier film of the above character which has a thickness in the range of 70-80 gauge.
Another object of the invention is to provide a barrier film of the above character which has decreased yield losses.
Another object of the invention is to provide a barrier film of the above character which will not curl.
Another object of the invention is to provide a barrier film of the above character which is a monolithic product that can be heat sealed onto itself.
Another object of the invention is to provide a barrier film of the above character which has low friction.
Another object of the invention is to provide a barrier film of the above character which is particularly suitable for tobacco products such as cigarettes.
Another object of the invention is to provide a barrier film of the above character which can be produced at a reduced cost.
Another object of the invention is to provide a barrier film of the above character which will tear in a straight line.
Another object of the invention is to provide a barrier film of the above character which does not require the use of aluminum.
Another object of the invention is to provide a barrier film of the above character which does not require the use of co-extruded polymeric films.
Another object of the invention is to provide a barrier film of the above character which reduces the total volume of plastic required.
Another object of the invention is to provide a barrier film of the above character which reduces the difficulty of recycling.
Another object of the invention is to provide a barrier film of the above character which can be utilized for food packaging which can be used in microwave ovens.
Another object of the invention is to provide a barrier film of the above character which uses a non-metal which can be utilized for packaging food which can be used in a microwave unit and still be transparent with a long shelf life.
Another object of the invention is to provide a barrier film of the above character in which PVDC need not be utilized as barrier materials.
Another object of the invention is to provide a barrier film of the above character which can maintain a given moisture content for contents packaged in the barrier film.
Another object of the invention is to provide a barrier film and method in which the barrier film can be produced in a roll coater at high production speeds.
Another object of the invention is to provide a barrier film of the above character which is provided with a heat seal layer so that it can be readily utilized as a self-sealing packaging material.
Another objection of the invention is to provide a barrier film of the above character which serves as an overwrap packaging film that will increase shelf life of moisture and oxygen sensitive products.